Cardiac output is a physiological parameter and can be expressed as a product of heart rate and stroke volume. Cardiac output can be measured by using a catheter to introduce saline in the pulmonary artery or right ventricular outflow tract and measuring a downstream temperature change.
One such approach, known as thermodilution uses a biased thermistor located at the tip of a multi-lumen balloon tipped catheter that is transvenously advanced into the right atrium, ventricle, and ultimately into the pulmonary artery. At which point, an indicator solution (such as normal saline) is injected into one of the lumens with the end-hole of the catheter positioned within the right atrium. The change in temperature is measured at the distal thermistor during and shortly after the completion of a hand injection procedure. This dilution is then integrated and a cardiac output is calculated. The method is based upon the Stewart-Hamilton equation.
Inaccuracies in measured cardiac output can be related to atypical anatomy, low blood flow states, and during times of advanced circulatory support such as extracorporeal membrane oxygenation (ECMO), and severe tricuspid regurgitation back into the atrium.
U.S. Pat. No. 8,016,766 refers to a central venous catheter assembly for measuring physiological data for cardiac output determination and a method of determining cardiac output.